Little is known about the molecular structure of chromatin and how chromatin controls transcription in normal and neoplastic cells. It can be postulated that the interaction between the nuclear proteins and DNA plays an important role. Work by Baserga and his group has shown that structural changes occur in the chromatin of fibroblasts transformed by a DNA tumor virus (SV40). This proposal extends this work into a study of chromatin structure and function in erythroleukemic cells produced in chickens with the erythroblastosis strain R virus. Chromatin will be separated into both active and inactive fractions so that meaningful comparisons can be made between the active regions of chromatin in neoplastic as compared to control erythroblasts. The methods will involve studying protein-DNA interactions in chromatin by indication of the surface nuclear proteins and subsequent separation of the iodinated histone and nonhistone (including contractile) proteins. In addition, the length of the DNA in the chromatin fractions accessible to external reporter molecules (dyes and nucleases) will be compared, followed by minimal DNase hydrolysis of the different chromatin fractions and isolation of the "masked" DNA fragments. The "accessible" regions of DNA will be isolated by binding an external ion to the accessible DNA phosphate groups, followed by digestion of the non-protected regions with nucleases and proteases and dissociation of the ion-DNA complex by high salt. The accessible DNA fragments will be separated by gel electrophoresis. In this manner, some idea as to the relative length of "buried" as opposed to "accessible" DNA lying within the different chromatin fractions will be determined and characterized. The model system will then be extended to study human hematopathology by a comparison of chromatin structure in lymphoblasts from lymphoblastic leukemic patients in crisis and in remission.